Even though the medical community largely credits the existing COVID-19 vaccines with finally bringing case numbers down nationwide, many have also questioned how long it might be before a booster shot would be needed to keep the shots effective. The emergence of the highly contagious Delta variant has health officials questioning this more urgently, as data on how much protection Johnson&Johnson's single shot or the Moderna and Pfizer vaccines' two-dose regimen offers against the new strain slowly comes in. But an official from the U.S. Centers for Disease Control and Prevention (CDC) is now warning that there may be "severe" side effects associated with a third shot of vaccine, pushing back on the idea a booster may be needed just yet.
During a press briefing on July 13, Jay Butler, deputy CDC director, cautioned that existing data shows that the second shot of a two-dose regimen was statistically when side effects were most likely to develop, warning that more data was needed to ensure a booster wouldn't create a potentially dangerous situation. "We're keenly interested in knowing whether or not a third dose may be associated with any higher risk of adverse reactions, particularly some of those more severe—although very rare—side effects," he said.
Butler added that while the need for a booster shot may not be pressing for the general population, he believes that those more susceptible to the virus, such as the elderly or other high-risk individuals, would be most likely to require the shots, Reuters reports. However, he added that data so far had not shown that immunity had diminished in people who received their shots when they first began rolling out in December and January.
Butler's statements come a week after Pfizer announced that it planned to ask regulators in the U.S. to authorize a third dose of its vaccine based on preliminary data that suggested the existing regimen's effectiveness might wane after six months. However, the pharmaceutical company said it would publish "more definitive data" in a peer-reviewed journal to substantiate their claims after health officials bristled at the planned request, Reuters reports.
"Both Pfizer and the U.S. government share a sense of urgency in staying ahead of the virus that causes COVID-19, and we also agree that the scientific data will dictate next steps in the rigorous regulatory process that we always follow," Sharon Castillo, a spokesperson for Pfizer, said in a statement.
Other top health officials have also pointed out that the sudden urgency for a booster shot may be premature. In a blog post last week, Francis Collins, MD, director of the National Institutes of Health (NIH), drew attention to a recent study that found people who received two dose mRNA vaccines such as Pfizer or Moderna may not need another shot "for quite some time, unless SARS-CoV-2 evolves into new forms or variants that can evade this vaccine-induced immunity."
Still, other experts pointed out that thanks to the Delta variant, the most pressing issue at the moment might actually be getting the first shot rather than pushing for a third. "At this point, the most important booster we need is to get people vaccinated," Carlos del Rio, MD, an infectious disease expert at Emory University in Atlanta, told The New York Times.